This project is a sub-study of the Washington Heights-Inwood Community Aging Project, which is a multidisciplinary, epidemiological study of Alzheimer's disease and related neurodegenerative disorders. We will obtain positron emission tomography scans and simultaneous x-ray computed tomography scans using Florbetaben from Bayer on a selection of ongoing participants who will be selected on the basis of change in plasma levels of amyloid beta over time. Approximately 200 participants will receive scans beginning in 2009 and in the 2010-2012 assessment wave and then again in a 2014-2015 assessment wave. Our intention is to examine whether uptake of Florbetaben in the brain varies as a function of previous history of change in plasma levels of amyloid beta in order to validate plasma amyloid beta as a viable biomarker for late onset Alzheimer's disease.